Sweetening process



July 27, 1954- A. J. BRANDEL SWEETENING PROCESS Filed July 23. 1949 BlLVHHJ.

(\l INVENTOR I Alberi J. Brandel ATTORNEYS LO N (BOLVIHOVOO OHMDVd MOO Patented July 27, 1954 UNITED STATES TENT OFFICE SWEETENING PROCESS Application July 23, 1949, Serial No. 106,420

Claims.

This invention relates to an improvement in lead sulfide sweetening of petroleum distillates.

The lead sulfide sweetening process has been in commercial use in the United States for a number of years. In the practice of the process, a petroleum disti1late is intimately contacted with an aqueous caustic treating solution containing insoluble lead sulfide in suspension. The aqueous solution of alkali preferably comprises a to B. caustic soda solution, although as low a con centration as 1 B. is operative. The more dilute caustic solutions give slower sweetening reaction rates. The amount of lead sulfide in suspension in the caustic solution may vary from to 2 pounds of lead sulfide per gallon of reagent. The preferred proportions are from 0.5 to 1 pound of lead sulfide per gallon. Alkali hydroxides other than sodium hydroxide, for example, potassium hydroxide, may be used in the aqueous portion of the treating agent. Additional ingredients such as agents which reduce the interfacial tension between oil and water may also be present in the treating agent. The sodium salts of phenols or other acidic bodies present in petroleum are examples of such interfacial tension-reducing agents.

In the practice of the process, a hydrocarbon distillate containing mercaptans is contacted with the lead sulfide-caustic treating agent in the presence of added air or oxygen. The amount of air is controlled according to the mercaptan content in order to keep the treating reagent in a balanced condition, one-fourth mol of oxygen being required for each mol of mercaptan sulfur contained in the distillate. The mechanism by which the lead sulfide sweetening process effects the sweetening of petroleum distillates is thought to follow the pattern set out in the following equations:

The treating solution is in a balanced condltion when substantially all of the lead is present in the form of lead sulfide, the amount of water-soluble lead compounds being ordinarily 0.003 pound of lead per gallon of reagent or less, and when only traces of soluble sulfides are present in the reagent. The mechanism of the sweetening process as indicated by the above equations requires that oxygen be contacted with the treating agent in amount sufficient to produce the sulfur necessary for reaction with lead mercaptides to produce disulfides and return the lead to the form of lead sulfide. Balance is maintained by adjusting the rate at which air is introduced in accordance with the mercaptan content of the feed and by introducing sodium sulfide as required to insure the necessary low con tent of water-soluble lead compounds. This process has been described in some detail in U. S. Patent 2,208,591.

In the commercial practice of the lead sulfide sweetening process, the formation of emulsions has frequently presented serious operating problems. When the feed and the treating agent form emulsions, the sweetening time is lengthened, lead sulfide is carried out of the treating plant with the finished product, and a drop of 5 to 7 numbers on the Saybolt color scale may be shown by the finished product. In the past, it has been the practice to meet the emulsion problem by reducing the feed rate to the lead sulfide treating plant. The reduction of feed rate ordinarily reduced or eliminated the emulsion difficulties, but obviously had an adverse effect on the throughput of the plant. On occasions the emulsion problem has become so severe that it has been necessary to pump the entire batch of emulsified treating reagent out of the plant into a storage tank, where it was subjected to a prolonged settling period, while a fresh charge of treating reagent was introduced into the plant. Neither of these methods provided an entirely satisfactory solution to the problem of emulsion formation.

It now has been found that the formation of emulsions during the lead sulfide sweetening process may be substantially completely elimi hated and that the feed rate and mercaptan tolerance in the feed can be increased by maintaining in solution in the treating agent a minor proportion, ordinarily between about 0.3% and 3% of sodium sulfonates prepared by sulfonating a fraction of the sulfur dioxide extract of kerosene and preferably recycling a suficient portion of the-sweetened product to the treater to reduce the mercaptan sulfur content of the mixture of fresh feed and sweetened product entering the treater to below about 0.02% by weight. The fraction of the extract which is sulfonated has a boiling range between about 4.00 and 530 F.

The resultant sulfonic acids are then neutralized with caustic soda.

The invention may be more completely understood by reference to the drawing, which is a diagrammatic illustration of the apparatus and process fiowemployed in the practice of this invention. Sodium hydroxide is introduced into mixing tank 3 via lines I and 2. Lead oxide 1s introduced into tank 3 through inlet line 4 and the sodium sulfonates referred to above, and more particularly described hereinafter, are in troduced into mixing tank 3 through line 5. The resulting mixture of doctor solution and sodium sulfonates is withdrawnfrom tank 3 through line 6 and is pumped into line I. Sodium sulfide is introduced into tank it) via line 52 and water is introduced into tank via line 9 to prepare a so dium sulfide solution. This solution is withdrawn from tank it through line i and passed via line i2 into blowcase !3. Air isintroduced into line It and is passed into b1owcase-.|3 toexpel the so dium sulfide solution from the blowcaseithrough line into line I. Feed is introduced into line It. and the feed from line it a-nd the treating-reagent, now consisting of sodium sulfide suspended in caustic, are drawn into pump 11, where they are intimately mixed andiorced through line i3 and loop mixer I9 into treater 20. Air is passed from line hi through line 2! into line it in amount necessary to keep the solution in balance. The mixture of feed and treating agent has a short residence period in treater 28; where partialphase separation is efiected. The overflow from treat-er 2% consisting of feed and treating agent, flows through line 22 into inclined settler 23. where the phase separation between the feed and treating agent becomes substantially complete. The treated distillate is withdrawn from settler 23 throughline 2i and is passed through a rockpacked coagulator 25,..where any minor proportions of lead sulfide which'may remain suspended in the product are removed. The sweetened feed is withdrawn from coagulator 25 through line 28 as .the process product. Treating agent settling outof the mixture of feed and treating agent in treater 28, i withdrawn from these vesselsvia lines 27.28,.and 29, respectivel and passedthrough reagent recirculation line .33 into linev 7.1 Lines 3!, 32, and 33 are illustrative of the provision made for handling liquid withdrawn from coagulator 25,.settler 23, and treater Ell-respectively. Each of these vessels is provided witha series of try cocks from which liquid-levelmay be determinedand-from which samples may be withdrawn. The liquids so withdrawn pass through line 34 into drip sump 35', from which this'material may be either withdrawn from the system via line 36-, returned to treater 25 via lines 1 and [5, or introduced into mixing tank 3 via, lines 3?- and2-.. Line 39 is provided for the return of a portion of the sweetened distillate to line. it to. dilute the feed andreduce the mercaptancontent of the oilentering pump- I? to below 0.02% by weightcalculated as mercaptan sulfur. This .linemay also be used to return off-test product to the system for further treatment. Line 38 is provided to :permit passage of sodium sulfide solution directly into line 2?. and thence intosettler23 as. required.

The .diificulties caused by the emulsions encountered prior to theernployment. of sodium sulfonates as a component of the treating reagent willbe readily appreciated to be serious upon inspectionof the fiowdiagram-set'out in the drawing.

The eificiencyof the particular odium sulfonates referred to above and describedin detail hereinafter to eliminate the emulsion problem and to increase sweetening capacity was tested. in a commercial lead sulfide treating plant proc-. essing 4000 barrels per day of a pentane-hexane settler 23, and in coagulator 25 is cut of thermally cracked naphtha. The sodium sulfonates were added to the treating agent in amount sufficient to constitute 1% of the reagent volume. After this addition the feed rate to the treating plant was increased from a previous maximum or about 4000 B./D., at which rate sweetening was sometimes incomplete and reagent losses-werahigh, to :1 0,00013; /D., at which rate. the treati'nglstock passed doctor and color tests and the reagent separation was excellent. During the run the mercaptan sulfur content of the feed was increased from 0.015% to 0.04% without encountering any resultant treating or operating.difiiculties although stocks of higher mercaptan contentare normally more difiicult tosweetenaandemulsify more readily with the treating reagent. The employment of this reagent wascontinued in a commercial scale unit for a'period of three months during which an average feed rate of 6000 B./D. was maintained and during which entirelysatisfactory sweetening was obtained without encountering any emule sion formation.

The sodium sulfonates which are employed in the process of this invention are preparedby the: followingv process. Kerosene is extracted .with sulfur dioxide. The. extract is distilled and .an approximately to cut. of. thev extract. is taken overhead. The overhead .hasan initial boiling point of about-400, F; andanendpoint not above 530 F. on an ASTM-D-BG distillation. This distillate is sulfonated by mixing. about 10 volumes of the distillate withapproxima-tely 6- volurnes of a .low viscosity. oil.such.:asaheavyx kerosene or a spray oil havinga-viscosity of about i 300 Sayboltseconds at 210 Ffthat. is inert to-- 98% sulfuric acid. The oilis: added toabsorb some. of the heat of reaction anda properly designed heat exchanger or cooling .coil may be used to control temperature, in which. case i the oilr addition may be elirriinated.v Eight volumesofi. -98 sulfuric acid are slowly. added to the mix-. ture of distillate and lowiviscosity oil-with agitae tion over aperiodof about.an-hour.- Coolin or the addition of.furtherlowviscosity oil, is re-- sorted to to maintain the temperature within :the approximate limits of to 1309.15. When the sulfona-tion is complete, aboutl5. volume per cent of water is added to the reaction mixtureiandethe resulting mixture is agitated for .a .short-period. Afterxa settlingtime of- 5 to .20 minutes; the lower weak-acid layer. drawn oil. Thesulfonic acid is then. neutralizednwith..33 Be. caustic to a pH'of 8 'to 10. After 4 to-5 hours. the unsaponifiable oilseparatesas. an upper oily. phase, and a lower aqueousphase-containingsulionates and sulfate is. transferred to. arcooling tank and co'oledto- 65 to 70 Atthistemperature, sodiumsulfate crystallizesfrom the solutionand a clear solution of the desired sodium sulfonates is obtained 1' by"decantation. If lower gravity causti'cl iszcused in neutralizing the sulfonic acid-the 'final concentration or 'sulfonates will be lower.

The kerosene -subjected .to $02. extraction' in the initial .step maybe obtained-irom any-eithercrude oils now-refined, inlarge volumesin this: country. Kerosenes frormwaxy crudes are :ordie-- narily used and 'thesulfbnates. prepared from r.

them are preferred. TheSOz.extractionisordie:- narily conducted Lat-temperatures V below- 50 Fr and .the volume of. S02 .per -volumeeof oil-.is in: the range 0.25.' .to...1.0..- It. is+the aromatic mate-v rials. extractable by 1 S02. which 2 are: desired for? sul fonation. and, while-SOais .the. preferred 501-1. I

vent. other solvents such as hydrofluoric acid, furfural, phenol, and acetonitrile yield extracts which may be processed as above described to produce the desired sulfonates. The sulfonates may be prepared by treating a suitable kerosene fraction with sulfuric acid, omitting the extraction step; however, it is preferred to employ the extract as the starting material.

The sodium sulfonate product has the following properties: It is a brown, free-pouring liquid which is miscible in all proportions with water and insoluble in hydrocarbons. It is an alkylaryl type sodium sulfonate with surface active properties.

Typical tests (content by weight) Sodium sulfonates 52.0% by weight. Water 45.5% by weight. Inorganic salts 2.5% by weight. Water insoluble 0.10% by weight. pH of 5% in water 9.

Appearance Clear, brown liquid. Specific gravity 1.203. Lbs. per gallon 10.0. Molecular weight of sodium sulfonates 2'70 (approx). Gardner viscosity, 25 C 0.4 poise.

As indicated previously, the sodium sulfonates are added to the lead sulfide treating agent in amounts between 0.3 and 3% by volume. This is on the basis of volumes of the aqueous sodium sulfonate solution described in the above table per volume of lead sulfide treating reagent. On a weight basis the amount of sulfonates added to the lead sulfide reagent is between about 0.15 and 1.5%. Amounts lower than 0.15% by weight do not effectively prevent emulsion formation and amounts appreciably in excess of 1.5% by weight have been found in some cases to aggravate rather than reduce emulsion difficulties.

The discovery that the particular sulfonate composition described above was effective in preventing the formation of emulsions during the lead sulfide treating process was made after a prolonged study of the emulsions formed and a correspondingly long experimental program in which a great many reagents, including a number of other sodium sulfonates, were tested in unsuccessful attempts to break the emulsions. No other reagent has been found which is effective for this purpose. A variety of commercially available emulsion-breakers, including a number of reagents sold under the trade name Trot-O- Lite, were tested without obtaining any beneficial result. Sodium sulfonates prepared by the sulfonation of other petroleum fractions and sulfur dioxide and phenol extracts of other petroleum fractions were ineffective in breaking the emulsions formed in the lead sulfide sweetening process. Various sulfonates prepared for use as commercial detergents, such as alkyl aryl sulfonates, were ineffective for this purpose.

The mechanism of the reaction by which the sodium sulfonates above described improve both the reagent separation and the sweetening characteristics of the reagent is not understood, but the results obtained show a marked and valuable improvement in the efficiency of the process.

I claim:

1. In the lead sulfide sweetening process, the improvement which comprises maintaining in solution in the lead sulfide treating agent a minor proportion, sufficient to inhibit emulsion 6 formation in the process, of sodium sulfonates prepared by sulfonating a fraction of a sulfur dioxide extract of kerosene boiling in the range of about 400530 F. and neutralizing the sulfonated product with caustic soda.

2. In a process for sweetening petroleum distillates comprising agitating the oil and air with a treating agent comprising a suspension of lead sulfide in an aqueous solution of an alkali metal hydroxide, the improvement which comprises maintaining in solution in the alkali metal hydroxide solution a minor proportion, sufficient to inhibit the formation of emulsions of the oil and treating agent, of sodium sulfonates prepared by sulfonating a fraction of a sulfur dioxide extract of kerosene, said fraction having a boiling range about 400-530 F., and neutralizing the resultant sulfonic acids with caustic soda.

3. In a process for sweetening gasolines and kerosenes comprising agitating the oil and air with a suspension of lead sulfide in caustic soda solution, the improvement which comprises maintaining in solution in the caustic soda solution a minor proportion not less than about 0.15% by weight of sodium sulfonates prepared by sulfonating a fraction of a sulfur dioxide extract of kerosene, said fraction having a boiling range of about 400-530 F. and neutralizing the resultant sulfonic acid with caustic soda.

4. In a process for sweetening mercaptancontaining petroleum distillates comprising agitating the distillates in a treating zone with a treating agent comprising lead sulfide suspended in an aqueous sodium hydroxide solution, the improved method which comprises recirculating a sufiicient amount of the sweetened product to the treating zone to reduce the mercaptan sulfur content of the total oil entering said zone to below 0.02% by weight, and maintaining in solution in the treating agent between about 0.15 and 1.5% by weight of sodium sulfonates prepared by extracting kerosene with sulfur dioxide, separating a fraction of the extract boiling in the range about 400 F. to 530 F., sulfonating said fraction by treating it with concentrated sulfuric acid at a temperature in the range about F. to F., and neutralizing the sulfonated product with caustic soda.

5. In a process for sweetening mercaptancontaining petroleum distillates which comprises agitating the oil and a treating agent comprising lead sulfide suspended in aqueous sodium hydroxide in a treating zone, the improved method which comprises maintaining in solution in the treating agent a minor proportion, sufficient to inhibit the formation of emulsions, of sodium sulfonates prepared by the steps comprising sulfonating a fraction of an S02 extract of kerosene boiling in the range about 400 F. to 530 F. with concentrated sulfuric acid at a temperature in the range about 120 to 130 F., separating the resulting sulfonic acids and neutralizing them with concentrated sodium hydroxide, separating the unsaponified oil from the aqueous phase containing sodium sulfonates, cooling the aqueous phase to 65'70 F. to crystallize sodium sulfate, and decanting an aqueous sodium sulfonate solution.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,208,505 Blair et a1. July 16, 1940 2,281,347 Blair Apr. 28, 1942 

1. IN THE LEAD SULFIDE SWEETENING PROCESS, THE IMPROVEMENT WHICH COMPRISES MAINTAINING IN SOLUTION IN THE LEAD SULFIDE TREATING AGENT A MINOR PROPORTION, SUFFICIENT TO INHIBIT EMULSION FORMATION IN THE PROCESS, OF SODIUM SULFONATES PREPARED BY SULFONATING A FRACTION OF SULFUR DIOXIDE EXTRACT OF KEROSENE BOILING IN THE RANGE 